JP2003270567A - Optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical scanner of a multi-beam deflection type whose high-speed applicability is made excellent by reducing a load to a deflector and in which multi-beam optical performance is made uniform on the same surface. <P>SOLUTION: A position at which the intervals of the principal rays of several laser beams A1, A2, B1 and B2 made incident on a deflection surface P4 in a subscanning direction are made minimum is set as P3 between a light source and the deflection surface P4. This is a condition to uniformize an optical characteristic, and because a position at which several laser beams are maximally converged is set on the side of the light source rather than on the deflection surface P4, angle differences in among the laser beams made incident on an fθ lens 20 in the subscanning direction are reduced, so that an image formation characteristic on a photoreceptor is made uniform. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device used in an electrophotographic color printer, a color copying machine or the like. More specifically, the present invention relates to an optical scanning device which is used in a tandem type full-color image forming apparatus and which exposes a plurality of photoconductors by scanning a plurality of laser beams with a single deflector.

[0002]

2. Description of the Related Art Electrophotographic color printers and color copying machines are widely used in offices. When a full-color image is formed by an electrophotographic method, a so-called 4-cycle type image forming apparatus is used in which an image is output after executing four image forming cycles using yellow, magenta, cyan, and black toners. Often. The 4-cycle method utilizes the conventional black and white (monochromatic) image forming process to realize colorization, but the image output speed is 1 for a black and white image forming apparatus.
It has a problem of falling below / 4.

In order to solve this problem, image forming portions having charging, exposing, developing and transferring functions are arranged in parallel for four colors, and yellow, magenta, cyan and black image formation is performed in one pass, and full color is obtained. An image forming apparatus called a tandem system, which forms one image at almost the same speed as black and white (single color), has been developed. However, the tandem-type full-color image forming apparatus developed in the early stage is large,
In addition, because of its high price, it was only popularized in some specific markets that prioritize speed.

However, with the development and spread of the Internet environment centered on the Internet, color business documents have been widely distributed and exchanged, and as a result of the widespread use of digital cameras in an instant, color documents and color images have become It is now handled normally in general offices. As a result, the occupancy rate of color originals increases, and the slow output speed of the 4-cycle color image forming apparatus is becoming a stress in the daily work of the office. Further, there has been a strong demand for a full-color image forming apparatus that can be installed in a work group unit in an office and has an installation space similar to that of a monochrome image forming apparatus.

As a device configuration that meets such a demand,
There is an image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2001-264655 by the present applicant. In this image forming apparatus, four photoconductors are arranged in parallel in the horizontal direction, and an optical scanning device is provided below the photoconductors.
An intermediate transfer belt is arranged above it.

A charging roll and a developing device are provided around each photoconductor, and an electrostatic latent image formed by exposure of a laser beam modulated according to image signals of yellow, magenta, cyan, and black is formed in each color. It is developed with the corresponding toner. When the intermediate transfer belt moves, the developed image is primarily transferred onto the intermediate transfer belt in the order of yellow, magenta, cyan, and black. Further, it is collectively transferred onto the paper fed from the paper tray at the secondary transfer point, finally heat-fixed by the fixing device and discharged as a full-color image.

In the image forming apparatus, in order to realize the same size reduction as that of the conventional black-and-white image forming apparatus, each unit constituting the image forming apparatus is downsized, and a method other than simple scale down is changed. ing.

Of these, the miniaturization of the optical scanning device will be described.

In the conventional tandem type image forming apparatus, a plurality of optical scanning devices are arranged corresponding to a plurality of photoconductors, but the image forming apparatus described above uses four laser beams with one deflector. Is adopted, and four laser beams are emitted from one housing.

As a result, not only the space of the deflector itself is reduced, but also the space inside the housing is shared by a plurality of laser beams, so that the optical scanning device becomes compact, and the space occupied in the image forming apparatus is greatly increased. Can be reduced to

An optical path layout for scanning a plurality of laser beams with a single deflector will be described below.

At the base point (light source) and the end point (photoreceptor) of the laser beam optical path, those corresponding to the respective colors are arranged apart from each other, so that the optical path layout is such that the laser beams emitted from the respective light sources are combined. Must be collected in the vicinity of a single deflector, and after deflection, they must be separated to be distributed to each photoconductor.

In order to realize this combination and separation, the above-mentioned optical scanning device makes two laser beams enter the deflector with an angular difference in the sub-scanning direction. Then, two laser beams are crossed in the vicinity of the deflector, and the optical paths are combined and separated by selective reflection using a folding mirror at positions before and after the deflector where the gap between the two laser beams becomes large.

Further, a laser beam deflected upward from a deflector arranged in the center of the housing is returned to the deflector direction by a common folding mirror, and then the laser beam is arranged corresponding to each laser beam. By folding back one by one by a folding mirror, the optical path is separated and the laser beam is guided to different photoconductors.

Another purpose of the optical path layout in which the two laser beams have an angular difference is the common use of optical components. The beam gap required for separation is determined regardless of the optical path layout, so if the beam optical paths are intersected in the middle of combining and separating, the two-beam interval near the deflector will be minimized and the thickness of the deflector will be reduced. It becomes possible to reduce the number of beams and to use two beams of the fθ lens.

FIG. 8 is a view showing an angle difference 2 in the sub-scanning direction.
FIG. 7 is a sub-scanning cross-sectional view for explaining an optical path layout when a book laser beam is incident on the deflection surface of a single deflector.

Reference numerals A and B respectively represent the chief rays of two laser beams. O represents the optical path optical axis of the optical system (optical system reference plane), and the rotation axis of the deflector 75 is the optical path optical axis O of the deflecting surface.
Is orthogonal to. The two laser beams A and B are incident on the optical axis O of the optical path at angles α and β (| β |> | α |> 0). The reason why | α |> 0 is that it is assumed that the incident beam to the deflector 75 and the deflected beam both pass through the fθ lens 77.

Although FIG. 8 shows the optical path expanded in the sub-scanning direction, the optical paths actually taken by the two laser beams pass through the fθ lens 77 from the a and b directions indicated by broken lines. Is incident on the deflecting surface P4 and reaches the separation folding mirror 79.

The optical path layout will be described according to the order of travel of the laser beam.

The laser beams A and B emitted from a light source (not shown) are laser beams B at the optical path combining position P1.
Only the reflected light is reflected by the combining folding mirror 81, and combined with the laser beam A so as to be close to each other in the sub-scanning direction.

The two combined laser beams A and B are
It intersects at a position Ρ3 in front of the deflection plane P4. The laser beams A and B having a slight gap on the deflecting surface P4 proceed while increasing the gap again, and only the laser beam A is reflected by the separating / folding mirror 79 at the optical path separating position P5, and travels to the photoconductor (not shown). The optical paths of the laser beam A and the laser beam B are separated.

There may be another optical component between Pl and P5 that does not change the mutual relationship of the two beams.

The crossing position of the two laser beams is located closer to the light source side than the deflecting surface of the deflector in order to minimize the angular difference between the two laser beams and to make the imaging characteristics uniform. For example, in the configuration shown in FIG. 8, α = 1.2 °, β
= 2.4 °, both the uniformity of the optical characteristics and the layout capable of combining and separating the optical paths can be achieved.

[0024]

As described above, the optical scanning device shown in FIG. 8 which bidirectionally scans two laser beams having an angular difference in the sub-scanning direction is miniaturized. By using common parts, the cost has been reduced and the optical characteristics of the four laser beams have been made uniform, but two sets of fθ lenses are required, and at least two beams must be used for synchronous detection. There is a limit to cost reduction.

Further, since the two surfaces of the deflector facing each other are scanned bidirectionally, two laser beams sandwiching the deflector are in the reverse direction, so that inversion processing of image data is required. Further, when color registration, which is important for a full-color image forming apparatus, is considered, two deviations due to temperature fluctuations, control errors, influences of various variations, etc. appear in opposite directions, and can be ignored because they have the same behavior in the same direction scanning. There is a problem that the configuration becomes complicated because registration deviation must be taken into consideration.

In order to solve these problems, it is considered that all the laser beams are deflected by the same deflecting surface and a plurality of photoconductors are exposed to improve the identity and commonality.
However, as described above, the problems become more complicated regarding the combination of combining and separating a plurality of beams and making the optical characteristics uniform.

As one for deflecting all the laser beams on the same deflecting surface and scanning a plurality of photoconductors, Japanese Patent Application Laid-Open No. 20-206 is disclosed.
00-347116, JP-A-7-256926, JP-A-2001-4948, and JP-A-2001-2001.
No. 281575 is available.

FIG. 9 is a block diagram of an optical scanning device disclosed in Japanese Patent Laid-Open No. 2000-347116. The laser beams emitted from the four independent light sources 60 are collected and deflected in the vicinity of the reflecting surface 62A of the polygon mirror 62.
The deflected laser beam is emitted by the cylindrical lens 64.
After being made parallel to each other, they are transmitted through the fθ lens 66 and guided to the respective photoconductors 70 by independent folding mirrors 68.

In this structure, since the four laser beams are gathered on the reflecting surface of the polygon mirror 62, the effective diameter in the sub-scanning direction of the reflecting surface 62A of the polygon mirror 62 becomes the minimum width, and the polygon motor is made thinner by making the polygon mirror thinner. Although it is excellent in reducing the load on the
The angle difference formed by the four laser beams in the sub-scanning direction becomes large, and it is very difficult to make the imaging characteristics of the four laser beams uniform.

FIG. 11 is a diagram showing an optical path development view of the optical scanning device described in Japanese Patent Laid-Open No. 7-256926. Four laser beams, each having a different angle in the sub-scanning direction with respect to the optical axis of the imaging optical system, are made incident on the deflecting surface 72 of the deflector in a state in which the principal rays converge. Since the four laser beams cross each other after passing through the deflector, the difference in the incident angle of the laser beams incident on the lens in the sub-scanning direction becomes large, and in order to make the imaging characteristics of the four laser beams uniform. It is necessary to take measures such as using a large aspherical lens 74.

FIG. 12 is a diagram showing a sub-scan section of the optical scanning device described in Japanese Patent Laid-Open No. 2001-4948.
The laser beams emitted from the four independent light sources are combined into four parallel laser beams by a prism, and the laser beams are incident on the polygon mirror 76 in a state parallel to the sub-scanning direction. Since the four laser beams can be incident on the imaging lens 78 without any angle difference, it is advantageous to ensure the uniformity of the optical characteristics. However, as shown in FIG. 13, the beam gap is on the polygon mirror and the optical path. Separation position (mirrors 80, 82, 8
4 position), the effective diameter of the reflecting surface 76A of the polygon mirror 76 in the sub-scanning direction becomes large, and a very thick polygon mirror is required.

In this structure, there is a problem that the processing is difficult because the load on the polygon motor is increased and the flatness of the entire reflecting surface is secured. An increase in the load on the polygon motor not only poses a problem in reliability such as vibration, noise, and heat generation, but also limits the applicability at high speeds (up the rotation speed).

As shown in FIG. 14, JP-A-2001-28
In the optical scanning device described in Japanese Patent No. 1575, four laser beams emitted from a semiconductor laser array are made incident on a polygon mirror 86 in a state of being parallelized by a transmission optical system.
The four deflected beams are separated into two beams by the first separating means 88, and are further separated by the folding mirrors 90 and 94 to be guided to the four photoconductors 92. This configuration is also disclosed in JP-A-200
As with the optical scanning device described in JP 1-4948A,
There is a problem that the processing becomes difficult because the load on the polygon motor is increased and the flatness of the entire reflecting surface is secured. Also, by using a semiconductor laser array,
Relative maintainability in which the fluctuations of the four beams occur together is improved, but there is a problem that the cost is high.

In view of the above circumstances, the present invention is for a multi-beam deflection type full-color image forming apparatus which can reduce the load on the deflector, is excellent in high-speed applicability, and has the same optical performance of a plurality of beams. An object is to provide an optical scanning device.

[0035]

An optical scanning device according to a first aspect of the present invention exposes a plurality of photoconductors by deflecting laser beams emitted from a plurality of independent light sources on the same deflecting surface of a deflector. In the optical scanning device for scanning, the position where the principal ray interval of the plurality of laser beams incident on the deflection surface in the sub-scanning direction is minimum is located between the light source and the deflection surface.

The above structure is a condition for making the optical characteristics uniform. By making the position where the plurality of laser beams most gather together on the light source side with respect to the deflection surface, the angle difference between the laser beams incident on the fθ lens in the sub-scanning direction can be reduced, and the image forming characteristics on the photoconductor can be reduced. Can be made uniform.

An optical scanning device according to a second aspect is characterized in that, of the plurality of laser beams incident on the deflection surface, two laser beams do not intersect on a sub-scanning cross section.

The above-described structure is a condition for facilitating the synthetic separation of the optical paths while reducing the angle difference between the plurality of laser beams in the sub-scanning direction. If the four laser beams are crossed and the composite separation is performed as in the conventional case, the angle difference between the laser beams inevitably becomes large, and it becomes difficult to make the optical characteristics uniform.

Therefore, as a method of ensuring the gap for the composite separation, the difference in the incident angle between the laser beams and the distance between the laser beams are used. That is, by not intersecting the optical paths, it is possible to create a gap between the laser beams required for the synthetic separation without increasing the angular difference.

An optical scanning device according to a third aspect of the invention is characterized in that the plurality of laser beams are four and two parallel two laser beams are provided.

The above-mentioned structure is a condition for minimizing the angle difference between the four laser beams. By maintaining the optimum parameters of the optical path layout with two laser beams, and by adding two laser beams parallel to each of the two laser beams, it is possible to achieve 4
While the two laser beams can be scanned, the angle difference between the laser beams can be made equal to that of the two laser beams, so that the imaging characteristics can be made uniform.

According to a fourth aspect of the present invention, the laser beam deflected by the same deflecting surface of the deflector is divided into optical paths by a reflecting mirror at positions where the principal ray intervals in the sub-scanning direction are substantially uniform. There is.

In the above structure, the reflecting mirror is arranged at a position where the principal ray gap formed by the difference in the incident angle between the plurality of laser beams and the distance between the laser beams becomes substantially equal, and the light is selectively reflected. The optical path can be easily split.

In the optical scanning device according to a fifth aspect, the laser beams emitted from the plurality of independent light sources are made into a laser beam group smaller than the number of the light sources by the first combining means, It is characterized in that it is made into a single-bundle laser beam by the synthesizing means and is incident on the same deflecting surface of the deflector.

The above-mentioned configuration is related to optical path synthesis. When the principal rays of the laser beams emitted from a plurality of independent light sources are converged in the vicinity of the deflector, two-stage synthesis is performed by the first synthesizing means and the second synthesizing means. Optical path synthesis can be facilitated.

According to a sixth aspect of the present invention, in the optical scanning device, the first synthesizing means is an optical path synthesizing method utilizing a principal ray gap in the sub-scanning direction, and the second synthesizing means is an incident angle difference in the main scanning direction. Is used for optical path synthesis, and the position where the principal ray interval of the plurality of beams in the sub-scanning direction is the minimum is substantially coincident with the position of the second combining means.

The above configuration is a condition for optimizing the layout for optical path synthesis. By combining the first optical path by the principal ray gap in the sub-scanning direction and the second optical path by the incident angle difference in the main scanning direction, it is possible to mount the light source and the combining optical system without expanding the required space. can do.

An optical scanning device according to a seventh aspect is characterized in that both the first combining means and the second combining means are plane mirrors.

In the above structure, the optical paths are combined by the selective reflection by the plane mirror, so that the structure can be simplified and the cost can be reduced.

In the optical scanning device according to the eighth aspect, a bundle of laser beams incident on the deflector is transmitted through the fθ lens and is incident on the same deflecting surface of the deflector, and after being deflected, it is again deflected. It is characterized in that it passes through the fθ lens.

The above-mentioned structure is related to the incident system to the deflector, and is a double-pass incident in which the light is transmitted through the fθ lens twice. By using a double pass, it is easy to ensure the symmetry of the optical characteristics with respect to the scanning center, the diameter of the deflector (polygon mirror) can be reduced, and the load on the polygon motor can be reduced. Further, it is possible to dispose the polygon mirror and the fθ lens close to each other, and the degree of freedom in designing the optical system can be increased.

According to a ninth aspect of the present invention, in the optical scanning device, the second combining means is located at a position returning from the deflecting surface to the light source side, and the distance from the deflecting surface to the first optical path dividing position is 0.6.
It is characterized in that it is separated from the deflecting surface by a distance of 2 times to 0.9 times.

The above-mentioned configuration relates to the arrangement of the folding mirror in double-pass incidence. The incident optical system (second combining means) in the double bath avoids interference with the deflected laser beam and the optical path separation mirror, and the laser beam incident on the plane orthogonal to the rotation axis of the deflector is This is a condition for optimizing the optical characteristics by minimizing the angle formed in the sub-scanning direction.

According to a tenth aspect of the present invention, in the optical scanning device, the second synthesizing means is arranged in such a direction that a laser beam group smaller than the number of the light sources synthesized by the first synthesizing means is folded back in the main scanning direction. The laser beam group farthest from the optical path optical axis of the deflecting surface when viewed in the sub-scanning direction is incident on the side closer to the deflector of the second combining means.

The above-described structure is a condition for defining the positional relationship in which the laser beam group synthesized by the first synthesizing means is made incident on the second synthesizing means (folding mirror) in double-pass incidence.

Since the laser beam group synthesized by the first synthesizing means is incident on the second synthesizing means with a distance in the sub-scanning direction, the margin with the laser beam deflected by the deflector is increased. , The laser beam group farthest from the optical axis of the optical path of the deflecting surface when viewed in the sub-scanning direction is made incident on the side closer to the deflector of the second combining means to optimize the layout and the optical performance. Can be compatible.

In the optical scanning device according to the eleventh aspect, the plurality of laser beams incident on the same deflecting surface of the deflector are:
The width of the laser beam in the main scanning direction is wider than the width of the deflecting surface. With the above configuration, the overfilled optical system reduces the diameter of the polygon mirror and increases the number of surfaces of the polygon mirror, thereby reducing the load on the polygon motor and providing an optical scanning device with excellent high-speed applicability.

[0058]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing a first embodiment of the present invention. FIG. 2 is a sub-scanning sectional view of an expanded optical path according to the first embodiment of the present invention.

As shown in FIG. 1, four independent light sources 1
The laser beams emitted from 0A1, 10A2, 10B1 and 10B2 are the plane mirror 12, which is the first combining means.
The light paths are combined by 14 and the number of light sources (4 in this embodiment)
Two laser beam groups A1A2, B1
It becomes B2.

The first combination of the laser beams A1 and A2 is performed by the laser beam A1 passing above the plane mirror 14 and the laser beam A2 being turned back by the plane mirror 14. The first combination of the laser beams B1 and B2 is performed by the laser beam B1 passing above the plane mirror 12 and the laser beam B2 being turned back by the plane mirror 12. Then, the combined laser beam groups A1A2 and B1B2 are
It is folded back in the main scanning direction by the common folding mirror 16.

On the reflecting surface of the plane mirror 16, a laser beam group B1B2 having a large distance from the laser beam deflected by the polygon mirror 18 is formed (a laser beam group B1B2 having a large distance from the optical path optical axis O of the deflecting surface). , Side closer to polygon mirror 18 on flat mirror 16 (narrower width)
Laser beam group A1A2 onto the plane mirror 1
The light is made incident on the side farther from the polygon mirror 18 on 6 (wider side).

As a result, the angle formed by the incident laser beam group with respect to the plane orthogonal to the rotation axis of the polygon mirror 18 can be suppressed, so that the interference between the incident laser beam and the deflected laser beam is avoided and the optical characteristics are stabilized. Can be converted.

Further, as shown in FIG. 1, the common folding mirror 16 as the second synthesizing means has a trapezoidal shape to prevent interference with the deflected laser beam. Further, as the function of the folding mirror 16, it is required to reliably fold the two sets of laser beam groups A1A2 and B1B2 toward the polygon mirror 18, so that a sufficient distance from the incident laser beam group to the mirror edge is secured. The mirror may have any shape as long as it is provided.
It is also possible to use a commonly used rectangular mirror and attach it by providing an oblique reference surface on a housing (not shown) for mounting the mirror.

The two sets of laser beam groups A1A2 and B1B2 turned back by the turning mirror 16 are transmitted through the two sets of fθ lenses 20 and are incident on the reflecting surface 18A of the polygon mirror 18.

On the optical path from the common folding mirror 16 to the reflecting surface 18A of the polygon mirror 18, the gap between the two laser beam groups A1A2 and B2B1 in the main scanning direction is gradually narrowed, and the reflecting surface 18A of the polygon mirror 18 is gradually reduced.
In the upper part, the principal ray of the laser beam is located almost at the center of the reflecting surface 18A and becomes four laser beams arranged in the sub-scanning direction.

Although an optical element is omitted in FIG. 1 in order to explain how the optical paths are combined, a collimator lens for converging divergent light from the light source is provided on the optical path from the light source to the polygon mirror. It includes a cylindrical lens that converges the laser beam only in the sub-scanning direction, and on the reflecting surface 18A of the polygon mirror 18, the laser beam forms a linear image extending in the main scanning direction. The two-sheet fθ lens 20 has power only in the main scanning direction, and is composed of a concave cylindrical surface and a flat surface, and a flat surface and a convex cylindrical surface, respectively.

With the above structure, four independent light sources 1 are provided.
Laser beams A1, A2, B1 and B2 emitted from 0A1, 10A2, 10B1 and 10B2 are flat mirrors 1.
2, 14 and polygon mirror 1 by folding mirror 16
8 are collected on the reflecting surface 18A.

The rotation of the polygon mirror 18 causes 4
The book laser beams A1, A2, B1, and B2 are deflected and scanned in the same direction. The four deflected laser beams A1, A2, B1, and B2 again pass through the fθ lens 20, pass above the common folding mirror 16, and reach the position of the plane mirror 22. When reaching the plane mirror 22, the four laser beams A1, A2, B1, B2
Have substantially equal intervals, and only the lowermost laser beam B1 is folded back by the plane mirror 22 to become the laser beam B1 directed to the photoconductor, and optical path separation is performed.

In FIG. 1, four laser beams are drawn in alignment in the main scanning direction for the purpose of explaining the laser beam gap, but two sets of laser beams are used for the main scanning surface with respect to the reflecting surface 18A of the polygon mirror 18. Since the light beams are incident at an angle within, the two light beams are separated in the main scanning direction at the same timing.
Scanning is performed as a set of laser beams, but if the image data is controlled according to the delay amount, a full-color image without misregistration can be formed.

In the example of the optical path layout in the optical scanning device 24 after the plurality of laser beams are deflected by the polygon mirror 18 shown in FIG. An image is formed on the photoconductor 32 by the mirror 26, but an image is formed on the photoconductor 32 by the two folding mirrors 28 and 30 as in the optical scanning device 34 shown in FIG. 4B. It is also possible to select appropriately.

Here, the optical path layout will be described in detail with reference to FIGS. 4 laser beams A
1, A2, B1 and B2 are optical paths in which the folding mirror 16 as the second synthesizing unit and the laser beam A2 and the laser beam B2 and the laser beam A1 and the laser beam B1 are parallel to each other. There is. Further, the laser beam A2, the laser beam A1, and the laser beam B2
And the laser beam B1 make an angle difference of 1.6 °
Is.

The beam gap (principal ray interval) required for the optical path separation (in the folding mirror 22) at the optical path separation position P5 is 4 mm, and the center position Ρ3 of the second combining means is set.
The deflection surface P4 (the reflection surface 1) is aligned with (the center of the folding mirror 16).
8A) in the direction returning to the light source side, when the distance L from the deflection surface P4 to the optical path separation position P5 is set to 0.8 times (128 mm), the laser beam incident on the deflection surface P4 and the laser beam deflected are set. The angle in the sub-scanning direction required for separation is 2.7 °.

Then, α and β with respect to the optical axis O of the optical path shown in FIG. 2 are 2.7 ° and 4.3 °, respectively.

This is larger than α = 1.2 ° and β = 2.4 ° in the case where two laser beams are deflected as shown in FIG. The uniformity of the optical characteristics of the laser beam can be ensured.

Further, as described above, the two fθ lenses 2
Since 0 has a power only in the main scanning direction, it exhibits the same image forming characteristics in the sub scanning direction regardless of the incident height of the laser beam, so that the uniformity of the optical characteristics can be secured.

It should be noted that when the value of α becomes large, it influences the increase of the scanning line curvature and the thickening of the beam diameter at both ends of the scanning area. However, the increase of the scanning curvature is caused by providing the curvature adjusting means after the optical path separation. The diameter increase can be made uniform by rotating the fθ lens around an axis parallel to the main scanning direction. Further, the black circles shown in the folding mirror 16 represent the reflection positions at which the laser beam group first synthesized by the plane mirror (not shown) is folded back by the plane mirror 16, and the ellipse on the left side thereof is The combination of laser beam groups is explicitly shown.

Next, the setting position P3 of the second synthesizing means, the thickness of the polygon mirror 18, and the homogenization of the optical characteristics will be described.

In the first embodiment, two sets of parallel laser beams are emitted from the deflecting surface P4 (reflecting surface 18A) to the optical path separation position P5 by 0.8 times the distance L, and the laser beams are returned from the deflecting surface P4. Are crossed. This position is made to coincide with the position where the distance between the principal rays of the four laser beams in the sub-scanning direction is minimum.

That is, the parallel laser beams A1 and B1
The optical system layout for optical path synthesis is optimized by matching the intersecting position of the other parallel laser beams A2 and B2 with the position of the second combining means. At this time, at the position of the deflecting surface P3, the gap between the two sets of parallel laser beams in the sub-scanning direction has begun to widen, and the principal ray interval on the deflecting surface P3 becomes 7.6 mm.

This is wider than when two laser beams intersect on the deflecting surface as shown in FIG. 8, but it is 12 mm (necessary when deflecting four parallel laser beams). Compared to the distance required for separation = spacing 4 mm × 3), it is sufficiently thin.

Further, if the overfilled scanning method is used, the diameter of the polygon mirror can be reduced, so that the load on the polygon motor can be reduced and high-speed applicability can be ensured.

Next, for comparison, an optical path layout in which priority is given to reducing the thickness of the polygon mirror will be described.

FIG. 5 shows two sets of parallel laser beams A1,
FIG. 3 is a diagram showing an optical path layout in which B1 and laser beams A2 and B2 intersect at a deflection plane Ρ4. The black ellipse in the figure represents the reflection position where the laser beam group is folded back by the plane mirror 16.

The optical path gap at the optical path separation position P5 requires a fixed amount (4 mm) regardless of the optical path layout, so 2
The optical path separation position P5 from the intersection of the pair of parallel laser beams
The shorter the distance is, the larger the angle difference between the two parallel laser beams.

In the example shown in FIG. 5, the angular difference in the sub-scanning direction is 2.9 °. At this time, the principal ray distance of the laser beam becomes large even at the beam combining position P3 returning from the deflecting surface P4 on the optical path, and when the combining optical system shown in FIG. 1 is configured, the common folding mirror 16 moves in the sub-scanning direction. It will be a big one. Further, the principal ray interval at the position where the first combining means is arranged is further widened, and a large space is required for mounting the light source and the combining means, resulting in a configuration that does not meet the original purpose of downsizing the optical scanning device. .

Thus, in consideration of the structure of the optical path combining system, the thickness of the polygon mirror, and the uniformity of the optical characteristics, the position at which the principal ray interval in the sub-scanning direction is minimized is
It is desirable to set it at a position returning from the deflecting surface to the light source side, and particularly when using the double-pass incidence method, the deflecting surface P
4 of the distance L from the optical path separation position P5 to 0.6.
It is desirable to set the position 9 times.

2 and 5, the case of two sets of parallel laser beams has been described, but it is not necessary that they are completely parallel, but it is desirable that the two sets of laser beams do not intersect each other. .

Here, the reason why it is not necessary to be completely parallel will be described.

When the optical path separation is performed by the plane mirror, the layout shown in FIG. 4 can be used as the layout of the entire scanning optical system. As you can see in Figure 4, and even looking at the conventional example,
The optical path separation is repeated one by one. Therefore, the distance required for optical path separation (for example, 4 mm) may be ensured at a position displaced in the traveling direction of the laser beams, and there is some degree of freedom in the principal ray relationship of the four laser beams in the sub-scanning direction. .

However, if the parallel relationship is greatly deviated,
All the laser beams intersect at a position behind the optical path separation position, the angle difference between the plurality of laser beams becomes large, the uniformity of optical characteristics is impaired, and optical path synthesis becomes difficult, resulting in a large It will require space. Therefore, it is desirable that the plurality of laser beams are composed of two sets of laser beams that do not intersect.

Here, the usefulness of this method will be described by comparison with a method different from the method using two sets of parallel laser beams.

FIG. 6 shows a set of parallel laser beams A
A set of laser beams A2 and B having an angle difference with B1 and B1.
2 shows an optical path layout using 2. At the intersection of the parallel laser beams A1 and B1 and the laser beams A2 and B2 having an angle difference from the deflection plane P4, the optical path separation position P5.
If the laser beam is installed at a position that is 0.8 times the distance L up to the deflection surface P4, the angle formed by the plurality of laser beams in the sub-scanning direction is the same as when two sets of parallel beams are combined. become. Further, the necessary width of the reflecting surface in the sub-scanning direction of the polygon mirror is also the same. Therefore, the same performance can be obtained in terms of uniformity of optical characteristics.

However, the principal ray relationships in the vicinity of the light source for performing the optical path composition are close to each other, and it is difficult to combine the beams with a simple configuration using a plane mirror. As described above, with respect to the problem of the optical path layout in which the laser beams emitted from a plurality of independent light sources are combined and collected in the vicinity of a single polygon mirror, and after being deflected, they are distributed to the respective photoconductors and separated. It is valid.

Next, a second embodiment of the present invention will be described.

FIG. 7 is a diagram showing an optical path layout in a sub-scan section when light enters the polygon mirror from outside the scanning range of the main scanning plane. Since it is not a double-pass incident,
The center lines O of the plurality of laser beams are in the plane orthogonal to the rotation axis of the polygon mirror, and α shown in FIG. 2 is 0.

Since the distance required for optical path separation and the position P3 of the second synthesizing means are the same as in the first embodiment, the relative relationship of the four laser beams does not change, and the two laser beams form one another. Is 1.6 °, and the chief ray distance on the deflecting surface is 7.6 mm. The difference from double-pass injection is f
Although the height of the θ lens 20 can be minimized, since the optical characteristics in the main scanning direction are not symmetrical with respect to the optical axis, an overfilled scanning system in which the light amount of the deflected laser beam changes depending on the deflection angle is used. Is not suitable for the combination of. Even when light is incident from outside the scanning range, two-step optical path combination in the sub-scanning direction and the main scanning direction is effective in order to simplify the configuration at the combining position.

[0097]

Since the present invention has the above-described structure, the load on the deflector can be reduced and the invention can be applied to high speed operation. Further, it is possible to make the optical performance of a plurality of beams uniform.

[Brief description of drawings]

FIG. 1 is a perspective view showing an optical scanning device according to a first embodiment.

FIG. 2 is a sub-scanning sectional view in which an optical path of the optical scanning device according to the first embodiment is expanded.

FIG. 3 is a schematic diagram showing a state in which four laser beams are deflected by a deflection surface.

FIG. 4 is a diagram showing an example of an optical path layout in the optical scanning device after deflecting a plurality of laser beams.

FIG. 5 is a diagram showing an optical path layout in which two sets of parallel laser beams intersect each other at a deflection surface.

FIG. 6 is a diagram showing an optical path layout of a pair of parallel laser beams and a pair of laser beams having an angle difference.

FIG. 7 is a diagram showing an optical path layout in a sub-scan section when light enters the deflector from outside the scanning range of the main scanning plane of the optical scanning device according to the second embodiment.

FIG. 8 is a sub-scanning cross-sectional view for explaining an optical path layout when two laser beams having an angle difference in the sub-scanning direction are made incident on a single deflector.

FIG. 9 is a configuration diagram of an optical scanning device described in Japanese Patent Laid-Open No. 2000-347116.

FIG. 10 is a schematic diagram showing a state in which four laser beams are deflected by a deflection surface.

FIG. 11 is a diagram showing an optical path development view of the optical scanning device described in JP-A-7-256926.

FIG. 12 is a view showing a sub-scanning section of the optical scanning device described in Japanese Patent Laid-Open No. 2001-4948.

FIG. 13 is a schematic diagram showing a state in which four laser beams are deflected by a deflecting surface.

FIG. 14 is a diagram showing a sub-scanning section of the optical scanning device described in Japanese Patent Laid-Open No. 2001-231575.

[Explanation of symbols]

12 Flat mirror (first synthesizing means) 14 Plane mirror (first combining means) 16 Folding mirror (second synthesizing means) 18 Polygon mirror (deflector) 22 Plane mirror (reflection mirror) 20 fθ lens

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/036 B41J 3/00 D 1/113 H04N 1/04 104A F term (reference) 2C362 AA07 AA10 BA04 BA50 BA51 BA54 BA61 BA83 BA84 BB03 2H045 AA01 BA22 BA34 CB33 DA02 5C051 AA02 CA07 DB22 DB24 DB30 DC04 5C072 AA03 DA02 DA04 HA02 HA06 HA09 HA13 HB10 QA14 XA05

Claims (11)

[Claims] 1. An optical scanning device for deflecting four or more laser beams emitted from a plurality of independent light sources on the same deflecting surface of a deflector to expose and scan a plurality of photoconductors. An optical scanning device characterized in that a position where a principal ray interval of a plurality of incident laser beams in a sub-scanning direction is minimum is provided between the light source and the deflecting surface. 2. The optical scanning device according to claim 1, wherein, of the plurality of laser beams incident on the deflection surface, two laser beams do not intersect on a sub-scanning cross section. 3. The four laser beams are four,
The optical scanning device according to claim 2, wherein there are two sets of two parallel laser beams. 4. The laser beam deflected by the same deflecting surface of the deflector is divided into optical paths by a reflecting mirror at positions where principal ray intervals in the sub-scanning direction are substantially uniform. The optical scanning device according to any one of claims 1 to 3. 5. The laser beams emitted from the plurality of independent light sources are made into a group of laser beams smaller than the number of the light sources by the first synthesizing means, and then the second synthesizing means makes a single-bundle laser beam. The optical scanning device according to claim 1, wherein the optical scanning device is made into a beam and is incident on the same deflecting surface of the deflector. 6. The first synthesizing means is optical path synthesizing using a principal ray gap in the sub-scanning direction, and the second synthesizing means is optical path synthesizing utilizing an incident angle difference in the main scanning direction.
6. The optical scanning device according to claim 5, wherein the position where the principal ray interval of the plurality of beams in the sub-scanning direction is the minimum is substantially the same as the position of the second combining unit. 7. The both of the first synthesizing means and the second synthesizing means are plane mirrors.
Alternatively, the optical scanning device according to claim 6. 8. A bundle of laser beams incident on the deflector is transmitted through the fθ lens, is incident on the same deflecting surface of the deflector, is deflected, and then is transmitted through the fθ lens again. The optical scanning device according to any one of claims 5 to 7. 9. The second synthesizing means is located at a position returning from the deflecting surface to the light source side, and has a distance of 0.6 to 0.9 times the distance from the deflecting surface to the first optical path splitting position. 9. The optical scanning device according to claim 5, wherein the optical scanning device is away from the surface. 10. The second synthesizing means is a plane mirror arranged so as to turn back a laser beam group smaller than the number of the light sources synthesized by the first synthesizing means in the main scanning direction, and the sub-scanning direction. 9. The laser beam group farthest from the optical axis of the deflecting surface when viewed in FIG. 6 is incident on the side closer to the deflector side of the second combining means. The optical scanning device described. 11. The plurality of laser beams incident on the same deflecting surface of the deflector have a laser beam width in the main scanning direction wider than the surface width of the deflecting surface.
11. The optical scanning device according to claim 10.